Method and apparatus for continuously coating a metal strand-like article with molten metal



1959 K. OGANOWSKI 2,914,419

METHOD AND APPARATUS FOR CONTINUOUSLY comma A METAL STRAND-LIKE ARTICLEwrm MOLTEN METAL I Filed Aug. 3. 1953 2 Sheets-5heet 1- INVENTOR. Msmwaawvams-m,

ATTORNEYS.

United States Patent:-

METHOD AND APPARATUS FOR CON'IINUOU SLY COATING A METAL STRAND-LIKEARTICLE WITH MOLTEN METAL Application August 3, 1953, Serial No.372,073"

29 Claims; (Cl. 117-7) The invention relates to the continuous coatingvof metal bodies in endless lengths with moltenmetal. I shall describethe invention inexemplary embodiments involving the coating of iron orsteel strip or wire with aluminum; but it will be understood that theinvention is not so limited but is applicable to the coating. of endlesslengths of strip' or wire of any metal with all of the molten coatingscurrent in the art, such as .zinc,'zinc containing minor amounts ofaluminum, tin, terne, alloys of aluminum and the like.

In the continuous hot coating of metal bodies, exemplary procedures incommercial use are'described in the Sendzimir Patents 2,110,893,2,136,957 and 2,197,- 622. In general, the scale-free strip or wire iscleaned as by the removal of oils, greases and the like, subjected to aheat treatment in a reducing atmosphere and carried beneath the surfaceof a bath of molten coating metal while still protected by the reducingatmosphere, so that no entrance flux need to employed. The metal to becoated is led into the coating bath at a temperature close to thetemperature of the bath itself; and the surfaces of the metallic strandare thus prepared for very rapid and thorough wettingby the molten metalitself;

In a specific though non-limiting procedure, iron' or steel strip inscale-free, cold rolled condition is first carried through an oxidizingfurnace wherein carbonaceous foreign matters are burned from the surfaceof the strip and an exceedingly thin, controlled coating of oxide isformed thereon. In the reducing furnace the thin oxide coating isreduced. Instead of the described treatment in an oxidizing'furnace,alkali or other chemical cleaning involving Wetting. and drying of thestrip surfacemay be practiced. Under certain operating conditions acoldrolled strip can be cleaned sufliciently by merely passing it intothe reducing furnace burning oif the carbonaceous foreign matters in aninitial section thereof; but pre-cleaning is preferred as a commercialprocedure;

Procedures just referred to are desirable for preparing the surface ofmetallic strands for the reception of coatings of molten protectivemetal. As hitherto practiced, however, the coating step has involved adipping procedure in which the metallic strands are passed through abath of the molten coating metal with which they remain in contact forappreciable but short intervals. As a consequence, themolten coatingmetal rapidlybecomes contaminated with the metal of the strands to becoated. For example, considerable quantities of dross will be formed ina zinc bath as well as in other bathsof'molten coating metal capable ofdissolving'iron; and in the case of aluminum or alloys rich inaluminum,-the bath rapidly becomes saturated with iron if iron is thematerial of the strand to be coated. The presence of large quantities ofiron in the molten aluminum is undesirable for several reasons. Forexample, coating with a bath presaturated with iron will make forlessductility and corrosion resistanc'e'in the coating, and gives riseto other difliculties.

The pick-up of iron by a bath of molten aluminum can occur from the potin which the bath is maintained and from guide, wiper and transfer-rollapparatus in the potjbut' this action progresses relatively slowly. Thecontamination of molten aluminum occurs in by far the greater proportionand shorter time by solution of iron from the surfaces of the strip orstrand which is carried through the pot. I believe this to be because ofthe extraordinarily ready solubility of the cleaned surfaces of thestrand in the aluminum and also because of the comparatively great areaof the strand surfaces exposed to the bath in a unit of time underconditions such that there canbe an interflow between aluminum which hasbeen brought against the strand and aluminum in the body of the bath. Itis for this reason that previous attempts to' minimize contamination ofthebath by diminishing the size of the bath with respect to the quantityof material carried therefrom on the strand have not been successful;The contamination of the bath by iron from the strand and the dilutionof the bath by addition of fresh" uncontaminated metal resultin theestablishment of an equilibrium concentration of iron in the bath whichmay approach saturation-ifthe immersion time is sufliciently long.Changing the size of the pot merely changes the timeznecessary forequilibrium to be reached. Much the same'thing occurs'with other'coatingmetals Where the base metal is soluble 'in them, or forms with themundesirable"contaminants;

Otherdifiicultie's arise in withdrawing the strand from the bath ofmolten coating metal; and the problem of making thin; uniformlycontrolled coatings has never hitherto satisfactorily been solved;Obviously there is littlecontrol if:the'strand merely is' withdrawn fromthe freesurface" of the bath; but theme of exit rolls (above the biteofwhicha meniscus of the molten coating metal collects)"-while animprovement, is not" fully satisfactory.

Attempts to scrape the surface of the strand after it has left the bathbutbeforethe coating metal has solidified are likely to result in'removal of coating down to an interface alloy, which is undesirable. Theproblem is greatly complicated when the coating metal is one, likealuminum and its alloys;-which readily forms tenacioussurface oxidefilms promoting theformation' of beads and ridges in the appliedcoating.

Yet again, the art has long desired a satisfactory mode of minimizingthe production of interface alloys.

Primary objectsof my invention are the provision of means and ametho'dfon forming: thin, uniform and controlled' coatings of good su'rfacecharacteristics, for controlling the-formation of interfacealloys',and-for increasing the-purity of coatings of metal as applied in moltencondition.

Itisan object of'one aspect of the'invention to provide a mode ofoperation and a coating apparatus in which the amount of coating metalapplied to the strand is the amount carried away by" the strand, therebeing no reflux of appli'edmetal to a bath,: so that bath contaminationis-g-reatlyreduced.

It is an object of this invention to provide a method of coating: astrand of metal withla molten coating metal wherein it is possible toreducethe exposure of the strand to; the molten coating metal to asufiiciently short time and to cool it so rapidly that'the interfacialalloy or compound formed is limited to a thin, uniform layer whichwillnot be deleterious to theadherence and ductility of the metalliccoating.

It-isa further object of this invention to provide a new aluminum coatedferrous product having superior coating. adherence and ductility as Wellas improved corro sio'n resistance, the aluminum coating layer of whichis attached to the base metal by a very thin, smooth and uniform"interfacial alloyor compound layer, the aluminun'ilayer itself beingmore uniform in thickness than has hitherto been possible. i v

.Another object of the invention is the provision of a means and methodwhereby bath oxide is prevented from interfering with coating by beingisolated from the metal increment which forms the actual coating.

Yet another object of this invention is the provision of means and amethod for applying molten coating metal to a strand-like metal base ina controlled and uniform manner resulting directly in a controlledcoating upon cooling.

These and other objects of the invention which will be set forthhereinafter or will be apparent to one skilled in the art upon readingthese specifications, I accomplish by that procedure and in the use ofthat apparatus of which I shall now describe exemplary embodiments.Reference is made to the accompanying drawings where- Figure 1 is apartial longitudinal section of a coating apparatus which I may use.

Figure 2 is a partial and semi-diagrammatic sectional view on a smallerscale showing the relation of the coating apparatus to a hood.

Figure 3 is a similar view showing a modified form of bath apparatus.

Figure 4 is a similar view showing yet another form of coating assembly.

Figure 5 is a longitudinal sectional view through a preferred apparatusused in practicing the invention.

Figure 6 is a sectional view through an applying device and stripshowing an upper lip extension reaching the gravitational level of themolten metal in the applying device.

Figure 7 is an enlarged detailed view through the ap-: plying device ofFigure 5.

Briefly, in the practice of one aspect of the invention I have foundthat it is practicable to applymolten coating metal to a metallic strandthrough the use of an applying device having a lip portion adjacent orcontacting the strand, in such a way that a thin, uniform coating isproduced in a controlled manner. The accomplishment of the function isdependent upon a plurality of factors as follows:

(1) A prerequisite for the application of a specific and controlledamount of the molten coating metal to strip material is that the lipelement exert a uniform pressure against the passing strip across anyface or area contacted by the lip. It must be kept in mind that therolled base metal may not only have variations in thickness, bothlongitudinally and laterally due to rolling conditions, but also may belongitudinally and laterally curved. To take care of such variations andto flatten the strip for contact with lip elements, it has been foundnecessary to produce a deflection in the strip while it is moving undertension in the coating apparatus. The means producing the deflectionsmay be the lip or the lips themselves, other elements located adjacentthe lips, or a combination of the lips and such other elements.

(2) The lips should preferably be adjustable in such fashion as to varythe pressure and the amount of deflection because this enables thethickness of the coating to be regulated within limits.

(3) The molten metal contacts the strip on one side of the lip element(usually, though not necessarily, the lower side, the strip usuallymoving upwardly). The strip leaves the lip element at its other side(usually the upper side for the same reasons) in coated condition. Sincethe lip is pressed against the strip, the molten coating metal in thethickness desired must pass between the strip and the lip against thepressure aforesaid. This occurs presumably through a filming action ofsome sort, the strip being thoroughly wetted by the molten coatingmetal. The specific amount of coating metal which passes between the lipand the strip is in this instance dependent primarily upon the pressureof the lip against the strip. The deflection of the strip by thepressure of the lip will produce the greatest flattening effect and 32-.

suit in the greatest uniformity of coating the more nearly the edge ofthe lip approaches a line contact with the strip. Optimum results areobtained by a very narrow flat lip edge with the plane of the fiat areasubstantially parallel to the strip.

(4) If more of the molten metal passes between the strip and the lipthan can be carried away by the strip, it will tend to collect at theother side of the lip in a meniscus or even to overflow the lip. Thiscan in part be controlled by varying the pressure as aforesaid; butanother and important element of control is to be found in operatingunder what I have herein termed negative pressure. In the apparatushereinafter described the lip elements are arranged to contact the stripalong lines above the gravitational top level of the molten metal in thecoating bath. The molten metal is drawn up into the space between theline of contact of the lip and the top level of the bath, by the filmingaction aforesaid, by capillarity or surface tension effects or otherwiseso that thehydrostatic pressure of the molten metal against the lip isless than it would be under conditions in which a gravitational headwere added. This is what I mean by the term negative pressure as usedherein and in the claims which follow. I have found that the thicknessof the coating produced is inversely affected by the amount of negativehead and furnishes another important means of control. p

The collection of molten metal at the free side of the lip element is tobe avoided since it will make for nonuniformity of coating, and willalso make for bead ng and ridging where coating is being done with ametal hke aluminum which rapidly forms tenacious oxide films.

The fundamental teachings of this application are not limited to thecoating of strip. In the coating, for example, of drawn wire, wherevariations in thickness, curvature, camber and the like are not apt tobe encountered, and where the material may be accurately guided, it willnot ordinarily be necessary to provlde for a deflection of the strand bythe lip elements. Furthermore, the lip structure may be redesigned toform a single element surrounding the wire, the wire passing through a.perforation in it. I shall, however, describe my invention in connectionwith exemplary embodiments which have to do with the coating of strip.By strip I mean rolled metallic bodies of indefinite length, usuallythough not necessarily of sheet thickness, and varying in width fromrelatively narrow strip in which, however, the width is a plurality oftimes the thickness, to strip of width suflicient for the formation ofcoated metal sheets of any commercial dimensions.

Under proper circumstances I have found it possible to form thin,uniform and completely controlled coatings of molten metal on base metalstrip without the collection of excess on the free side of the lip, andwith no irregularities due to the formation of excess oxide film, thestrip carrying away with it all the molten coating metal which passesbetween the strip and the lip.

Translated into terms of apparatus, the teachings above may take theform shown in any of Figures 1 to 4 inclusive.

The preparation of the metallic surfaces of the strandlike material tobe coated, e.g. ferrous strip or wire, is of primary importance in myprocess, as it is in any continuous coating procedure. The conditionscontemplated in the reducing furnace and the subsequent cooling hood arethe same as those set forth in the patents referred to above. It may bepointed out that the strip will be raised in the reducing furnace totemperatures at which a strong reducing effect will be obtained; but forspecial effects, such as annealing, normalizing, or softening by themethod of the copending application of Robert S. Burns and Robert L.Solter, Serial No.

and Steel Sheet Stock, the temperature may ,be raised to whatever valueis desired.

A cooling hood is employed to lower the temperature of the strand to avalue not far from that of the melting point of the coating metal andpreferably but not necessarily below it, to facilitate the rapid coolingafter coating. For example, in coating with pure aluminum, which has amelting point of about 1215 F., I may have the strip at about 115 ,F.and the molten aluminum at about 1350 F. It is desirable to adjust thetemperature of the strand and of the coating metal to such arelationship that complete wetting is obtained with the lowest possibleheat content of the composite mass. Particularly in coating heaviergages, beneficial results are obtained if the entering strip temperatureis as low as around 950-1000 F., and to get rapid wetting the moltenaluminum is raised considerably above its melting point even to as highas 1400 or l450 Referring first to Figure 2, I have shown in adiagrammatic fashion a strip 1 passing through a cooling hood "2 andinto a bath of molten metal 3 in a vessel 4, through a hell 5 which dipsbeneath thesurface of the molten coating metal and therefore protectsthe strip 1 from oxidation. As shown in Figure l the edged lips orpressure members 6 and 7 are displaced vertically with respect to eachother and exert pressure against the strip 1 so as to deflect it in itsvertical travel. In the particular embodiment illustrated the strip istensioned between a lower roll 8 and an upper roll 9, as will be evidentin Figure 2.

In order to provide for the elements of control discussed above, the lipelements 6 and 7 are mounted in the 'way next described. Base plates 10and 11 are mounted in opposite pairs on the sides of the molten metalcontainers 4 or on independent foundations. Supporting elements 12 and'13 are mounted for horizontal sliding movement toward and away from thestrip 1 on the base plates 10 and 11, their positions being adjustableby means .of screws 14 and 15. The supporting elements have overhangingportions 12a and 13a; and brackets 16 and 17 are mounted so as to bevertically slidable on dowels 18 and 19 on the supports. The verticalpositions of the brackets 16 and 17 are made adjustable by means ofscrews 20 and 21.

Shafts 22 and 23 extend across between respective pairs of the brackets16 and 17, and the lip elements 6 and 7 are mounted on these shafts bymeans of arms 24 and 25, as many of which may be provided as requiredfor stiffness. The angular positions of the lip elements 6 and 7 may beadjusted by turning the shafts 22 and 23 or by adjusting the positionsof the arms 24 and 25 on the shafts if the shafts are fixed, asindicated in Figure 1. The tips of the lip elements, indicated at 6a and7a, may be made of special metal of non-wearing characteristics such forexample as molybdenum; the trips are edged as shown. They contact thestrip 1 along lines vertically above the gravitational top level of thebath .3. This top level is indicated at 26. Due to the action explainedabove, the molten metal will be drawn up into .the spaces 27 and 28above the top level of the bath. The lip elements 6 and 7 will keep anyfilm of oxide forming on the top surface of the bath away from thestrip 1. The strip is shown as deflected or bent where it passes betweenthe tips 6a and 7a of the lip elements for reasons already given. Thedrawings are dimensionally exaggerated for clarity.

The described mechanism permits control of the weight and thickness ofthe coating in a desired range irrespective of variations in gage,speed, and tension of the coated strip. For example, with a given speedand ten- .sion of the strip an increased weight of coating may beattained either by lowering the lip members toward the normal bathsurface, or by decreasing the pressure of the lip tips against the stripand the consequent degree of deflection, providing sufficient deflectionis maintained to flatten the strip. Differential adjustment of thecoating coatings of molten metal.

on the two sides of .the strip is also possible. For example, in orderto decrease the weight of coating on one side of the strip the pressureof the lip on that side may be increased by moving the lip toward thestrip and increasing the deflection produced by it. At the same time thelip element on the opposite side of the strip may be moved slightly backso that the "weight of the coating formed on the second side is notchanged.

The adjustment of the height of the lips above the free bath surface,and the adjustment of their pressure against the strand, permit a widerange of weights of coating for a wide range of gages to be attained.For heavier gages the vertical displacement between the tips of the lipelements may be somewhat increased so that excessive pressures are notnecessary in order to obtain straight line contact of the lips with thestrip.

In Figure 3 I have shown ashallow and relatively small vessel 29 for themolten metal supported directly on an upturned portion 30 of the coolinghood 2. The strip 1 enters the molten coating bath 3 through an orificein the bottom of the vessel 29, so closely dimensioned to the strip 1 orprovided with suitable seals so that the molten metal will not draindown into the hood. Here the length of the path of travel of the stripthrough the molten metal may be greatly diminished and the volume of themolten metal in the vessel 29 greatly cut down.

A modified form of apparatus is illustrated in Figure 4 where a pan 31is affixed to the hood, the upward extension 30 of the hood openingthrough the pan. The vessel 32 for the molten coating bath is providedwith floats 33 and 34 so that it may be supported upon a molten leadbath 35 in the pan .31. The strip 1 again enters the vessel 32 through aslotin the bottom of it; and the path of travel of the strip through themolten coating metal is very short. In both Figures 3 and 4 the lipelements are again indicated at 6 and 7.

I have described above means and an operating procedure resulting in theimposition of thin controlled [In some embodiments the length of time ofcontact between the prepared surface of the strand and the bath ofmolten coating metal is minimized. The growth of an interface alloylayer between the base metal and the coating metal is largely a functionof the time of contact between the two metals when one of them ismolten. But inasmuch as the growth of an alloy layer with many metals,such particularly as aluminum, is very rapid, and inasmuch as theinterface alloy layer continues to grow after the coated strand has lefta molten coating bath during a period of time when the coating metal isliquid, it will be seen that a rapid cooling of the coated strand maybecome as important as a short immersion time and that optimum resultswill be obtained if both are reduced .to an absolute minimum. and amethod of procedure for accomplishing this, utilizing principles setforth above in combination with other factors.

It should be pointed out that the finishing of the coating is of greatimportance in minimizing contact time. If the coating is relativelythick or is irregular in thickness, the coated strand .cannot be asrapidly and uniformly cooled as otherwise. Yet again, the use ofconventional coating pots and exit apparatus such as exit rollsinterfere with the use of means for rapidly cooling the coated material.In the practice of my invention in its preferred form, the provision ofmeans operating on the principles set forth above for forming thin,uniform and controlled coatings permits the concurrent adoption ofpractices which reduce the time of contact between the base metal andthe coating when molten to very short intervals. In practice, I amproducing materials in which thetotal time of contact between dissimilarmetals When one of them is molten is below two seconds.

I am also enabled through a combination of factors I shall ,now describeapparatus to employ a coating method in which the molten coating metalis applied to the strand only in such quantities as can be carried awayby the strand, so that there is no reflux of molten coating metalbetween the surfaces of the strand and a reservoir or bath of the moltencoating metal. Under these circumstances the supply of molten coatingmetal does not become appreciably con taminated with metal dissolvedfrom the strand, and the coated strip can be cooled so quickly as toresult in an alloy layer of controlled thickness.

Figure shows a preferred form of apparatus which I have developed tolimit the contact of the base metal with the coating metal while it isin the molten condition to as short a time as possible to limit theamount of alloying while still producing a uniform and controlled weightof coating.

In Figure 5 I have not illustrated the portions of the Sendzimirapparatus lying in advance of the cooling hood. The strip 1 is shown aspassing through the cooling hood 2 which may be regarded as attached tothe Sendzimir reducing furnace by means of the flange 36. The strippasses beneath a roll 37 inside the hood and exits vertically to a driveroll 38 or other suitable propulsion and tensioning apparatus locatedbeyond the coating point.

The strip or strand emerges from the hood vertically through a slot ornozzle element 40 which is accurately positioned in an exit piece 41.The lower end of the exit piece is located in a trough or basin-likeelement 42, through which the upper part of the gas-tight hood 2 extendsand to which it is welded. The basin 42 is filled with molten lead toefiect a gas-tight seal between the hood and the exit piece 41. It willbe provided with electric or other heating elements to keep the lead inmolten condition, and will further be provided with an insulative casingas shown.

An inner cover member 43 with an opening for the passage of the strandis employed to restrict the escape of gas from the hood during threadingor at such other times as it is found necessary to remove the exit piece41 when the hood is filled with reducing gas. The inner cover 43 isremovable and is sealed in the same way as the exit piece 41. Theopening in the upper end or exit part of the hood should be large enoughto permit the removal of the roll 37, its bearings and preferably ascraper 44. The scraper is employed on the roll 37 to keep the surfacethereof smooth and free of scale particles or other accumulations whichmight make indentations in the hot strip passing around the roll undertension. It will be understood that while normally the strip 1 will beperfectly clean as it reaches the roll 37, provision must be made forthe removal of scale and the like from the hood and apparatus duringperiods of starting up, when an oxided strip may be passing through theapparatus before the atmosphere in the reducing furnace has attained aproper reducing activity.

A plate 45 may be welded at an angle inside the hood to deflect thestrip 1 under the roll 37 during threading operations.

I locate pipes 46 on either side of the upper extension of the hood 2and opening to the interior of the hood. The pipes may be welded to thehood proper with a slot or slots in each pipe coinciding with slots inthe hood wall. They are employed to feed vaporized sodium into theinside of the hood 2. Sodium is vaporized preferably at about 1075 F. ina separate furnace or retort and is carried to the hood through thepipes 46 by dissociated ammonia gas or other reducing gas employed inthe hood. The vaporized sodium is employed to control the reactionproduct between aluminum and the reducing gas atmosphere, so that acoating can be applied to the strand which is continuous and free fromnonwetted areas, in accordance with the teachings of Patent 2,437,919 inthe name of Oganowski. In the case of coating with other molten metals,the vaporized sodium i 8 is frequently used for scavenging the reducingatmosphere within the hood and furnace.

The mode of applying the molten .metal to the strand, as hereinafterdescribed, may be practiced entirely within the hood 2. I do not preferto do so because the applicators then become inaccessible or lessreadily accessible for purposes of adjusting, cleaning and the like, andmore difiiculty is had with the rapid cooling of the strip. I have foundit entirely possible to coat the metallic strand 1, outside the hood 2,by apparatus illustrated in the drawings hereof. Precautions must betaken, as hereinafter described to protect the surfaces of the strand upto the coating point.

Containers for the molten coating metal (aluminum in the exemplaryembodiment) are indicated at 47 and 48, and are hereinafter referred toas applicators. They are located on either side of the strand above thenozzle 40 of the exit piece 41. Electric or other heaters 49' areattached to these applicators to provide suflicient controlled heateither for melting the aluminum or for bolding it in molten conditiondepending upon the method of charging the aluminum or other coatingmetal into the applicators. It is within the scope of the invention tomelt the aluminum or other coating metal in a separate furnace or ladleand to convey it to the applicators 47 and 48, preferably by conduitmeans having an automatic valve control for maintaining a desired levelof the molten coating metal in the applicators. Each applicator has amouth indicated at 47a and 48a in Figure 5, through which the moltencoating metal is fed or siphoned to the surfaces of the strand 1 in wayshereinafter explained.

In Figure 5 in connection with the vessel 47 a diagrammatic showing hasbeen made of means whereby the vessel may be tilted and whereby it maybe adjusted toward and away from the strip 1. Thus the vessel isindicated as pivoted at 57 to a nut 58 riding on a threaded shaft 59which is journaled into a support 60 on a base. Movement of the threadedshaft 59 will carry the vessel toward and away from the strip. The nut58 has an extension 61 with a shaft 62 threaded therein and engaging thevessel at a point spaced from the pivot point 57. Adjustment of thethreaded shaft 62 will produce a tilting of the vessel about the pivotin either direction.

In the particular apparatus shown, where the coating of the strip occursoutside the hood, it is important that reducing gas from the hood flowthrough the nozzle 40 about the strand or strands and that its flow beso adjusted that the strand-like material is completely enveloped by thereducing atmosphere up to the point at which it is contacted by themolten coating metal. The spacing of the coating portions of theapplicators 47 and 48 from the end of the nozzle element 40' may dependon variables such as the strip gage and tension, the degree of stripdeflection required to attain the desired lip pressure, and the amountof reducing gas issuing from the nozzle. In all cases it is necessary tohave them close enough to the end of the nozzle to preserve anon-oxidized condition of the strand surface until the coating isapplied. Dry, oxygen-free reducing gas, such as hydrogen or dissociatedammonia, from a source outside the hood can be fed into the spacebetween the applicators and the nozzle for additional surface protectionif desired. I have found that in the particular apparatus employed byme, it is readily possible to protect the strip by means of gas issuingfrom the hood if the coating portions of the applicators are located notmuch more than about 1 /2 in. above the end of the nozzle 40.

Gas finishing pipes 50 may be located immediately above the coatingportions of the applicators. A protective gas is delivered through thesepipes and is fed from them through perforations extending across thelength of the coating portions. Preferably the pipes are supported bymeans providing precise adjustment in all planes, and the gas ispreferably directed at the contact point between the strand and thecoating portions of the applicators. The function of the finishing gasis to control the rate of oxide formation on the molten coating metal asit is carried away by the issuing strand. Natural gas has been used mosteffectively as a gas finishing atmosphere, although other non-oxidizinggases may be employed. It is not certain just how the finishing gasoperates, but using the gas finish, I have had no ditficulty in aluminumcoating without the breaking of oxide films and the formation of teardrops.

. It will be understood that the reducing gas issuing through the nozzle40 from the hood 2 as Well as the gas used for gas finishing issuingthrough the pipes 50, is preferably burning.

Upwardly directed scoops 51 are located on both sides of the strandimmediately above the applicators 47 and 48, and conduct low pressureair at or below room temperature to the surface of the strand in largevolume to freeze thereon the coating as fast as possible. As one skilledin the art will readily understand, the number of scoops required Willvary with the gage and speed of the strand, with the temperature of theair, with its volume and the like, and these factors may be controlledto pro duce the desired rate of cooling. Other cooling means, such ascompressed air applied through perforated pipes may be used, as well assteam sprays, water sprays, and water cooled rolls alone or incombination. If the bottom angle of contact between the cooling air andthe strip be not greater than about 30, there will be no interferencewith the gas finishing even though the air scoops are located, as shown,quite close to the pipes 50.

As has already been pointed out, the purpose of rapid cooling has to dowith the control of the alloy layer. Previous attempts to limit thethickness of the alloy layer in aluminum coating steel strips primarilyhave taken the direction of adding certain elements to the aluminum bathwhich suppress alloy formation, such as silicon or beryllium. They havenot been completely satisfactory. The addition of alloying elements tothe coating bath has lowered the ductility of the coating, decreased itscorrosion resistance, and in the case of beryllium, presented a healthhazard.

.Below the freezing point of aluminum, the rate of alloy formation issufficiently slow to have a negligible effect On adherence provided thestrip is cooled to less than 500 F. within a reasonable length of time,roughly not i more than about a minute and a half. In my process thetotal time of contact between the strand and the molten metal is cut. tothe absolute minimum, as hereinafter explained. Under the conditionsdescribed there .Will

"alwaysbe an interface alloy layer suflicient for good bond, becausealuminum reacts almost instantaneously with a steel strip surface whichhas been thoroughly cleaned and is at a temperature suitable forcomplete wetting.

The precise way in which aluminum alloys withiron is not completelyunderstood. Apparently one or more iron-aluminum alloys of definitecomposition are formed at the interface between the base metal and thecoating. "The instant formation of these alloys is capable of robbing:the coating metal of some of its iron content if it is initiallycontaminated with iron, as indicated by the fact 'that in quick frozencoatings produced in ways hitherto ties of the coated product aregreatly impaired if the interface alloy becomes too thick.

Using the new method and apparatus, I have beenable to reduce thelength'of time the strip is in contact molten aluminum so that the alloyis controlled to a very thin, smooth, uniform layer without the use ofalloying additions to the coating metal. This has madeit possible forthe first time to produce an aluminum coating of uniform and controlledthickness on iron or steel by a continuous process without the use ofalloying ingredients which will simultaneously have excellent ductility,adherence and corrosion resistance.

I have already indicated that in ordinary coating processes the pick-upof iron in the molten coating metal in the coating pot is largely due tosolution of iron from the strand itself. Solution of iron from the potand its appurtenances is much slower and theoretically could beminimized or overcome for a given rate of replenishment by diminishingthe relative size of the molten bath. In the process of the preferredaspect of this invention solution or iron from the strand into aresident bath of the molten coating metal is prevented. Thus, making theapplicators small in volumetric capacity in relation to the quantity ofaluminum passing through them will be effective in greatly minimizingsolution of iron into the aluminum from the applicators themselves.,However, it is within the scope of my invention to make the applicatorsof non-contaminating material such, for example, as of ceramics or ofmetals or alloys which do not dissolve readily in molten aluminum. Thereare various alloys having such property, and I may use any of them. Byway of example, molybdenum or alloys high in molybdenurn may be used.

The coating portions or mouths of the applicators are provided with apair of lips. Referring now to Figure 6, I have shown one form ofconstruction in which the lower lip 52 forms an extension of one edge ofthe applicator 47. It will be noted that the lip proper in this. figureis shown as lying substantially above the level of the molten coatingmetal 53 in the applicator. The upper lip, indicated at 54, is providedwith an extension 55 carried downwardly to a position below the toplevel of the molten coating metal. Assuming that the applicator is onedesigned for coating strip, the lip elements will be elongated in thedirection of the transverse dimension of the strip 1 as much as may benecessary to coat its width, and the upper lip element 54 and itsextension 55 may be thought of as fastened or welded to the. endportions' of the applicator 47. There is thus a channel indicated at 56between the lower lip and the upper'lip and its extension, this channelforming a sort of spout extending in the figure above the top level ofthe body of molten coating metal in the applicator 47 The uncoated striprides against the outer surface of the lower lip 52 and the coated stripagainst the outer surface of the upper lip 54; and by reference toFigure 5, it can be seen that the strip may be confined between the lipsof the opposite applicators 47 and 48, so as to be'defiected thereby,and so that these lips, acting together, guide and flatten the strip insuch manner-that the applicators remain in contact with it at all times.

In Figures 5, 6 and 7 the lips are dimensionally exaggerated for thesake of clarity. In the present practice of my process the contactingportion of each lip is about of an inch wide and the upper and lowerlips are spaced from each other a distance of of an inch. The totaleffective thickness of'the two lips and the space between them is .225inch. These dimensions are illus- Zt'rative only. It will be understoodthat the contacting portions of the lips may be reducedportions ofmetallic elements which are of-substantially greater thi'cknessforstrength, the elements being beveled or tapered to provide contactingportions of the desired thickness. I

The upper and lower lips preferably terminate toward the strip in asingle plane. The applicators are'arranged so as to have adjustingmovement toward and away from each other so as to secure the desireddeflection-oftlie 11 strip and the proper line contact of the lipstherewith. The applicators have adjusting tilting movements so as tobring both the upper and lower lips into the proper contact with theslightly deflected strip.

The spout may be filled by temporarily raising the level of the moltenmetal in the applicator until it fills the spout and contacts the stripbetween the upper and lower lips. Mechanical adjustments are providedfor the precise positioning of the applicators. These include means fortilting the applicator as well as means for adjusting it in thehorizontaland in the vertical planes, as has been indicated.

It will be understood that the surfaces of the metal strip 1 have beenprepared in such a way and are at such a temperature as to be veryreadily wet by the molten metal in the applicator 47. It will beunderstood that'the strip is moving in the direction of the arrow andthat the width of the orifice formed between the two lips is so narrowthat any metal applied to the strand will be carried away from theapplicator by the strand.

In order to control to the best effect the application of the metal tothe strand thinly and uniformly, I have found it advisable to operateunder conditions of negative gravitational pressure, as explained above.I have indicated that the metal level in the applicator is raised untilthe metal is brought against the surface of the strand. When this hashappened, however, and when the surface of the strand has been Wetted bythe molten metal, I lower the metal level in the open portion of theapplicator so as to bring the orifice between the two lips again abovethe gravitational top level of the molten metal in the applicator. Themolten metal, however, continues to fill the passageway 56 and to flowthrough this passageway to the surface of the strip, and it continues tobe carried away thereby.

A simplified form of applicator is shown in Figure 7. Here the upper lipelement 54 is provided wholly located above the gravitational top levelof the molten metal in the applicator, but there is no lip extensioncorresponding to the element 55 of Figure 6. Instead, reliance is hadupon a film of oxide 56 which forms on the surface of the bath andconnects the gravitational surface of the bath with the lip member 54.The lip member 54, how ever, keeps this oxide film from contact with thecoating formed upon the strand, so that no oxide is carried out of thebath onto the strand and the only oxide formed upon the surface of thestrand is that controlled by the finishing gas issuing from pipes 50, aspreviously explained.

The lips 52 and 54 may be made from a material which possessesresistance to attack from the molten coating metal. Where aluminum isthe coating substance, the material of these lips should preferably bewettable by molten aluminum, but should not alloy too rapidly withaluminum since otherwise it will erode away excessively and requirefrequent replacement. Also, the material should have good wearresistance as well as a low coefiicient of friction with the stranditself, so that the coating can be applied uniformly and without anygalling between the strand and the lips. When'coating iron or steel withmolten aluminum (and this is inclusive of all coating alloys containingaluminum as a major ingredient) molybdenum and cast iron are examples ofmaterials which can be used to make the coating lips. The contour of thecoating lips should be precise so as, for example,

. to maintain the same relationship between the lips and between thelips and the strand, all across the area of the strand which is beingcoated by the applicator. While I have shown opposed applicators forsimultaneously coating both sides of a strip, it will be evidentthat myapparatus is useful in instances where only one side of a strip need becoated, where a single applicator only is used, and where the strand isheld against the applicator lipsby a suitable substitute guide anddeflecting means on the opposite side. Also, it is within the purview of12 the invention to coat opposite sides of a strip with dilferjentcoating metals, as will be evident. 1

The aspects of control in the formation of thin, uni form coatings withthe apparatus of Figures 5 to 7 inclusive are essentially similar tothose discussed in connec: tion with Figures 1 to 4 above. It isessential that the upper lip of each applicator be pressed against thesurface of the strand and that the strand be deflected sumciently tobring about uniform line contact under sub stantially uniform pressurebetween the strand and the lip. Pressure and the degree of deflectioncan be varied by moving the applicators toward and away from the strip.The applicators will normally be displaced one from another vertically.Thickness of coating can be adjusted as before by control of pressureand by control of the amount of negative head. The upper lip of theapplicators will be preferably configured and edged such that the stripcontacting surface is not thicker than ,5; inch and will generally givebest results when around inch thick or less. It is also in the purviewof the invention to provide for a tilting of the upper lip with respectto its applicator.

Modifications may be made in the invention without departing from thespirit of it. Having thus described the invention in certain exemplaryembodiments, what I claim as new and desire to secure by Letters Patentis:

l. A process of continuously coating a metal strandlike article withmolten coating metal which comprises cleaning the strand-like article,and while the article is in the cleaned condition, moving said articlepast a memher having a lip against which the article moves, contactingthe article with molten coating metal at the approach side only of saidlip, said molten coating metal being derived from a source thereof, saidsource having a top gravitational level which is located below the levelof said lip, the movement of the article acting to carry a thin film ofthe molten coating metal between said article and said lip, maintainingsaid molten coating metal at the approach side of said lip in continuouscontact with the metal in said source so as to form a continuous body ofthe molten coating metal extending from said top gravitational level ofsaid source upwardly to said lip, the surface of said body located awayfrom said article being an unbroken upward extension of the surface ofthe metal in said source at said gravitational level, and isolated fromair at said surface, the weight of said body of molten coating metalbeing opposed to the passage of said molten coating metal between saidlip and said article, and said member having a portion adjacent saidlip, which portion is so located as to contact any film of oxidefloating on the said source of molten coating metal to keep said filmfrom contacting said article.

2. The process claimed in claim 1 wherein the strandlike article is astrip, in which the lip member is an elongated element and in which thelip member is pressed against the strip in such fashion as to deflectit, the strip being tensioned in its passage past the lip member.

3. The process claimed in claim 2 wherein'the lip member has a definiteedge and in which the amount of molten coating metal passing between thestrip and the lip member is controlled in part at least by varying thepressure between the strip and an adjacent portion of the lip member. I

4. The process claimed in claim 3 in which the strip is coated on bothsides through the use of two lip members offset from each other in thedirection of motion of the strip and each producingan oppositedeflection therein.

5. The process claimed in claim 4 wherein each lip member is a part ofan applicator having a second lip member closely adjacent to but spacedfrom the first mentioned lip member, the molten coating metalbeingconfined between the lip members of each applicaton.

6. The process claimed in claim 5 in which the coated 13 jstripisrapidlycooled immediately beyond said first mentioned lips.

7. A process of continuously coating a strand-like article with moltencoatingmetal which comprises cleaning the strand-like article and whilethe article is in the cleaned condition, applying the molten coatingmetal thereto from a source while the strand-like article is in motion,the application of the molten coating metal .being confined by lipelements contacting thesame side of said article and spaced from eachother by a distance so short in the direction of motion of saidstrand-like article that the molten coating metal applied thereto iscarried away thereby without opportunity'for; reflux to said source, thesaid molten coating metal at the point of application being higher thanthe gravitational level of the molten metal in said source.

8. A process of coating a moving strand-like metal article with moltencoating metal which comprises thoroughly cleaning the said strand-likearticle and heating it, providing a source of molten coating metal,applying said molten coating metal to the strand like article at aposition above the gravitational top level of the molten coating metalin said source, by providing a passageway between the said source andthe point of application of said molten metal, which passageway ischaracterized by lips spaced in the direction of motion of said article,said passageway being closed to the external atmosphere and causing thewithdrawal of the molten coatingtnetal from said point of applicationand the .end of said passageway by the said strand-like article movingin ,contact with said lips to produce a flow of .the said molten metaltherethrough.

9. The process claimed in claim 8 wherein said source of molten coatingmetal is a pan-like. container, one of said lips forming an edge of saidcontainer, and the other of said lips, spaced from the first mentionedlip in the direction of motion of said article, having an extensionpassing downwardly into said molten coating metal in said pan-likecontainer below the top gravitational level thereof, said extension,said lips and-adjacent walls of said container forming a closedpassageway irom the body of said molten coating metal to saidstrand-like article, through which passageway the molten coating metalis drawn under negative pressure.

10. The process claimed in claim 9 wherein the said strand-like articleis in the form of strip and wherein a second similar pan-like containeris located on the side of the strip opposite the first mentionedcontainer, the strip being guided and deflected by the lips of the firstmentioned container and the lips of the second mentioned container,whereby the lips of said containers maintain line contact with saidarticle.

11. The process claimed in claim 9 wherein the said strand-like articleis in the form of strip and wherein 14 the said molten metalthrough saidpassageway in the one direction only. 14. The process claimedwin claim-13 wherein the strand-like article immediately after coating is@surrounded by a non-oxidizing atmosphere.

15. A process of coating a moving strand-like metal articlewith moltencoating metal which comprises thora second similar pan-like container islocated on the side of the strip opposite the first mentioned container,the strip being guided and deflected by the lips of the first mentionedcontainer and the lips of the second mentioned container, and whereinsaid strip immediately after coating is surrounded by a non-oxidizingatmosphere.

12. The process claimed in claim 9 wherein the said strand-like articleis in the form of strip and wherein a second similar pan-like containeris located on the side of the strip opposite the first mentionedcontainer, the strip being guided and deflected by the lips of the firstmentioned container and the lips of the second mentioned container, andwherein said strip immediately after coating is surrounded by anon-oxidizing atmosphere, and is thereafter rapidly cooled.

13. The process claimed in claim 8 wherein the molten coating metal isapplied to the said strand-like article in a transverse area so short inthe direction of motion of the said strand-like article as to enforce aflow of oughly cleaning said strand-like article and raising itstemperature, providing a pan-like container having leading and trailingspaced lips, maintaining a bath of molten coating metal in said pan-likecontainer, moving said strand-like article past and in contact with saidlips, causing said molten coating metal to flow by'gravity and contactsaid article between said lips whereby to coat it, and while saidarticle is ina state ofcontinuous motion, bringing the gravitationalupper level of the molten coating metal in said container to a positionbelow the level of the-said lips, during acontinuation of the aforesaidcoating, whereby saidmolten coating metal is caused to travelupwardlyalong aportion of. said container to the trailing lip.

16; The process claimed in claim 15 wherein the said strand-like articleis in the form of strip and wherein asecond pan-like container islocated on the side of the strip opposite the first mentioned container,.the

strip being guided and deflected by the lips of thefirst mentionedcontainer and the lips of the second mentioned container, and whereinsaid strip immediately after coating 1 issurrounded by a non-oxidizingatmosphere, the said strip being surrounded by a non-oxidizingatmosphere from the point at which it is cleaned to the point at whichit is coated.

17. In coating apparatus for coating a strip with molten metal, meansfor moving a strip in .a path, :a source of molten coating metal, thesaid metal therein'having a gravitational upper level, a lip memberhaving an approach .and withdrawal side with respect to said movingstrip, means for pressing said lip member against said-strip so as todeflect it from said path, .and means rnetal on theapproach side only ofsaid lip member whereby a film of molten coating metal formed on thesurface of said strip is carried between said strip and said lip memberagainst said pressure, the said molten metal on the said approach sideof said lip member being higher than said gravitational upper level,said lip member having a portion spaced from said strip and extendingdownwardly below said gravitational upper level whereby to enclose acontinuous body of the molten metal extending above said gravitationalupper level, the weight of which body is opposed to the passage of themolten coating metal between said strip and said lip member.

18. Apparatus as claimed in claim 17 including means for adjusting therelationship between said lip member and said strip.

19. Apparatus as claimed in claim 17 including a second lip element inclose proximity to the first, the said molten metal as applied to saidstrand beinginitially confined between said lip elements to so narroweran area in the direction of motion of said strand as to enforce flow ofmolten metal in one direction only.

20. Apparatus as claimed in claim 17 including means for adjusting saidlip member toward and away from said strip whereby to vary saidpressure.

21. Apparatus as claimed in claim 20 including means on the oppositeside of said strip and offset from said lip member in the direction ofstrip movement, said means and said lip member acting to deflect saidstrip and maintain line contact between said lip member and ber ofelongated form adjacent a face of said strip and mounted with respect tosaid vessel. so that the edge of said lip member adjacent said strip isabove the gravitational level of the molten metal in said vessel, whilethe opposite edge is therebelow, means for adjusting said lip membertoward and away from said strip, means for tilting said lip member, andabutment means located on the opposite side of said strip, for holdingsaid strip against said lip member.

23. The structure claimed in claim 22 in which said abutment means isanother similar but oppositely directed lip member, longitudinallydisplaced from said first lip member and having a similar adjustabilityand relationship to the molten metal in avessel.

24. In apparatus for coating a metal strip with molten metal, a vesseladapted to contain a bath of molten metal, said vessel having at oneside a pair of closely spaced lips, the space between said lips beingopen to the interior of said vessel, means for moving a cleaned metalstripin a path outside said vessel but so located as to bring said stripin contact with said lips, and means for varying the gravitational levelof a bath of molten metal within said vessel so as to cause said moltenmetal first to pass gravitationally between said lips to contact saidstrip and thereafter to pass upwardly against the force of gravity overone of said lips so as to continue to contact and coat the said strip,the said lips being located so close together as to define a body of themolten coating metal which will remain continuous and unbroken in itsextent above the gravitational upper level of said bath so long as saidmoving strip remains in contact with said lip, the other said lip actingto contact any film of oxide floating on said bath to keep said filmfrom contacting said strip.

'25. The structure claimed in claim 24 wherein the means for varyingsaid upper gravitational level of said bath is a tiltable mounting meansfor said vessel.

26. The structure claimed in claim 25 -in combination with means forcleaning the strip including means to raise its temperature and hoodmeans to surround it with anon-oxidizing atmosphere, the said vesselbeing 16 located beyond the termination of said hood means and means forbathing said strip in a' non-oxidizing atmosphere from the terminationof said hood means to the point at which said strip contacts said lips.

27; The structure claimed in claim 25 wherein a sec.- ond similarvesselis positioned on the opposite side of said article and said article isconfined, guided and deflected by the lips of the said vessels. I

28. The structure claimed in claim 25 wherein a second similar vessel ispositioned on the opposite side of said article and said article isconfined, guided and deflected by the lips of the said vessels, andincluding means for surrounding the said article with a protectivenon-oxidizing atmosphere for a portion of its travel immediately beyondthe said vessels.

29. The structure claimed in claim 25 wherein a second similar vessel ispositionedon the opposite side of said article and said article isconfined, guided and deflected by the lips of the said vessels,including means for surrounding the said article'with a protectivenonoxidizing atmosphere for a portion of its travel immediately beyondthe said vessels, and including means for delivering a cooling fluidagainst the said article immediately after it has been coated.

7 References Cited in the file of this patent -UNITED STATES PATENTS1,496,309 Girvin June 3, 1924- 1,933,401 Ward Oct. 31, 1933 2,046,596Zwiebel July 7, 1936 72,062,795 5 Pike Dec. 1, 1936 2,095,718 SimmonsOct. 12, 1937 2,110,893 Sendzimir Mar. 15, 1938 2,111,826 Waltman et al.Mar. 22, 1938 2,398,034 ..Oganowski Apr. 9, 1946 2,536,186 Keller Jan.2, 1951 2,649,756 Egee et al Aug. 25, 1953 2,649,758 Cowgill Aug. 25,1953 2,681,294 Beguin June 15, 1954 2,772,518 Whitehurst et a1 Dec. 4,1956 Ha -a

1. A PROCESS OF CONTINUOUSLY COATING A METAL STRANDLIKE ARTICLE WITHMOLTEN COATING METAL WHICH COMPRISES CLEANING THE STRAND-LIKE ARTICLE,AND WHILE THE ARTICLE IS IN THE CLEANED CONDITION, MOVING SAID ARTICLEPAST A MEMBER HAVING A LIP AGAINST WHICH ARTICLE MOVES, CONTACTING THEARTICLE WITH MOLTEN COATING METAL AT THE APPROACH SIDE ONLY OF SAID LIP,SAID MOLTEN COATING METAL BEING DERIVED FROM A SOURCE THEREOF, SAIDSOURCE HAVING A TOP GRAVITATIONAL LEVEL WHICH IS LOCATED BELOW THE LEVELOF SAID LIP, THE MOVEMENT OF THE ARTICLE ACTING TO CARRY A THIN FILM OFTHE MOLTEN COATING METAL BETWEEN SAID ARTICLE AND SAID LIP, MAINTAININGSAID MOLTEN COATING METAL AT THE APPROACH SIDE OF SAID LIP IN CONTINOUSCONTACT WITH THE METAL IN SAID SOURCE SO AS TO FORM A CONTINUOUS BODY OFTHE MOLTEN COATING METAL EXTENDING FROM SAID TOP GRAVITATIONAL LEVEL OFSAID SOURCE UPWARDLY TO SAID LIP, THE SURFACE OF SAID BODY LOCATED AWAYFROM SAID ARTICLE BEING AN UNBROKEN UPWARD EXTENSION OF THE SURFACE OFTHE METAL IN SAID SOURCE OF SAID GRAVITATIONAL LEVEL, AND ISOLATED FROMAIR AT SAID SURFACE, THE WEIGHT OF SAID BODY OF MOLTEN COATING METALBEING OPPOSED TO THE PASSAGE OF SAID MOLTEN COATING METAL BETWEEN SAIDLIP AND SAID ARTICLE, AND SAID MEMBER HAVING A PORTION ADJACENT SAIDLIP, WHICH PORTION IS SO LOCATED AS TO CONTACT ANY FILM OF OXIDEFLOATING ON THE SAID SOURCE OF MOLTEN COATING METAL TO KEEP SAID FILMFROM CONTACTING SAID ARTICLE.
 2. THE PROCESS CLAIMED IN CLAIM 1 WHEREINTHE STRANDLIKE ARTICLE IS A STRIP, IN WHICH THE LIP MEMBER IS ANELONGATED ELEMENT AND IN WHICH THE LIP MEMBER IS PRESSED AGAINST THESTRIP IN SUCH FASHION AS TO DEFLECT IT, THE STRIP BEING TENSIONED IN ITSPASSAGE PAST THE LIP MEMBER.